Solder is commonly used for attaching dies to substrates. Bonding voids, however, are sometimes formed in the solder, due at least in part to the non-wettability of solder-to-die backside metal. The void problem may be particularly evident when a die has backside vias used for connecting one or more layers of the die to the backside metal layer, as the voids sometimes have a tendency to aggregate around the vias, due to air becoming trapped in the area around the vias. During solder reflow at elevated temperatures, the air around the vias expands, limiting the flow of solder to the area around the vias, resulting in voids. To avoid such voids, a scrubbing motion or vacuum solder reflow system may be used to help move the molten solder around to fill the voids created by the trapped air. Although void occurrence may be reduced by these methods, voids may still be present.